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#11
I'd be very dubious of buying an OS that came on a USB Flash drive. I don't know of any way to check it but I wouldn't risk spending money on one.
I got Windows 7 when it first came out through the pre-order offer and it was a full retail copy on discs in the official case with the key inside. Of course it now sits in storage as I don't use 7 anymore and don't have it on any machines here.